If you apply S90 after the soil temp has fallen below 60 degrees in the fall I believe that less than 20% will be is sulfate form by the first of April. S90 needs temps higher than 75 degrees to oxidize quickly. I would bet that 17821x chart of oxidization rates is with temps much higher than what you would have during the Nov thru March time. It is likely that 20% will be in sulfate form prior to the 21st of June.